Analysis of LDPC coded FSO communication system over correlated gamma-gamma turbulence channel for space shift keying modulation

Abstract

In free space optical communication (FSO) communication, it is assumed that the fading due to atmosphere turbulence (AT) is uncorrelated at the receiver. But, in practice the spacing between the receivers is less than the fading correlation length. So, we have to consider a correlated statistical model for FSO AT model. In this paper, we have analyzed space shift keying (SSK) modulation scheme over correlated Gamma-Gamma (GG) fading model. We have derived an average bit error rate (ABER) using moment generating function (MGF) for space shift keying modulation scheme over correlated Gamma-Gamma (GG) fading model. The system is analyzed for different atmospheric conditions, correlation values and different number of receivers. It can be observed that as we increase the correlation value, the ABER value deteriorates. It can be observed that the ABER does not depend on turbulence at low SNR, but for high SNR the ABER performance improves and the ABER performance is approximate same in weak and moderate turbulence. However, the difference of SNR between moderate and strong turbulence is approximate 5 dB for ABER value of 10⁻⁴. We note that at a given SNR, the ABER improves as we increase the number of receivers. Also, it can be observed that the ABER deteriorates as correlation increases for same number of receivers. We have also analyzed the system both uncoded and LDPC coded SSK transmitter systems. It is observed that for ABER value of 10⁻⁴, the SNR difference between LDPC coding and without encoding is approximate 3 dB.